I have a fermentation fridge that is large enough for two carboys and I have one in there now (a red) that is through primary fermentation. I have been ramping up the temp 1F a day and will continue to do so till I hit 67F which is where I would like to ferment my porter.

The Q

I want to brew a porter and add it to the fridge, swapping the temp probe to the new brew, but I know that as the fermentation heats up, the red will likely drop below 67 as the fridge tries to keep the porter at temp. The drop in temp will tell the remaining yeast in the red to flock out and I don't know how big of an effect this may have.

Details

The red will have been fermenting for ten days at this point, I have not taken a FG reading yet.

If the primary fermentation is done with the red....then it doesn't really matter what you do. You can leave it in the chamber with the porter or take it out and sit it in a closet. Once the primary fermentation is done, temperature isn't that important. Having said this, I don't mean extremes. Nothing like 100F or 20F. That's just silly....